Gripper devices



July 5, 1960 T. a. HAWKES GRIPPER DEVICES Original Filed April 1, 1953 3SheetsSheet 1 v S M mm 3 R m mm N A k QN Wm H m, QV m R m n um N H w mmmw & m w E Q M r M r: 1% uw m 7 z w\ Julyf5', 1960- 'r. B. HAWKESGRIPPER mavr czs 3 Sheets-Sheet 2 Original Filed April 1, 1953 INVENTOR.THU/MS BLAIR HAWKES y -196 T. B. HAwkEs 2,943,666

GRIPPER DEVICES Original Filed April 1, 1953 r v v 3 Sheets-Sheet 3INVENTOR. 77/0MA5 BLAIR HAWKES BY WV United States Patent UfiFice2,943,666 Patented July 5, 1960 GRIPPER DEVICES Thomas Blair Hawkes,'315 Trumbull Road, Manhasset, N.Y.

Original application Apr. 1, 1953, Ser. No. 346,164. Dligided and thisapplication Sept. 27, 1956, Ser. No. '6 ,536

'3 Claims. (Cl. 153-48) blank or shape must be gripped so that the metaltherebetween can be tensioned sufiiciently to elongate the materialbeyond its elastic limit, thereby imparting a permanent set thereto. Inone form of stretching machine,

two sets of gripper devices adapted to clamp the ends of a the metalsheet are disposed on either side of a central table for the formingdie. The table is carried on hydraulic rams Whose rise and fall areunder the control of the operator. Provision is made to hold the sheettan-. gentially to the curvature of the die and to stretch the sheet toa degree approaching the yield point on the material whereby uponrelease of the gripper devices the work retains the shape of the die.There are other forms of such machines, and a stretcher leveler alsorequires the use of gripper.

Gripper devices are usually constituted by opposing jaws which serve toclamp the end of the metal blank. When the workpieces are of Widelyvarying shape and size, conventional gripper devices are incapable ofconforming to the contour of the workpiece, as a result of which thegripping action is uneven and certain portions of the workpiece areinadequately clamped.

Another difficulty experienced with conventional gripping devices arisesfrom the fact that the pull of the workpiece, in the course ofstretching, exerts a lateral force on the jaws, thereby tending to shiftthe upper jaw relative to the lower jaw. This displacement produces amismatch of the jaws and hampers the gripping action. Furthermore, whenthe pressure exerted downwardly on the upper jaw is by means of ahydraulic piston operating within a cylinder, the lateral forcesproduced by the pull of the workpiece tend to displace the piston fromits axial position within the cylinder. This displacement is injuriousto the mechanism of the hydraulic apparatus and acts to score andotherwise mar the cylinder wall and the surface of the piston.

Wedge type grippers using a wedge angle adequate for good holding power,require long linear motion of the wedges. This makes a bulky,inconvenient, arrangement. The present invention provides a more compactform with the same or greater holding power.

In view of the foregoing, it is an object of this invention to providean improved gripper device having jaws adapted efliciently to grasp barsor sheets of varying size and shape.

More particularly, it is an object of the invention to provide a gripperdevice constituted by an upper jaw which cooperates with a lower jaw andis adapted to assume a profile conforming to the upper surface of ametal., bla nk having a non-uniform thickness. A significant per deviceoperates efiectively with sheets tapering in thickness from one side tothe other, or whose edges are warped and buckled. Prior art wedge ortoggle type grippers do not provide a large enough jaw opening in suchcases.

Yet another object of the invention is to provide a gripper devicehaving interengaging upper and lower jaws adapted to resist lateralstresses tending to displace the jaws. Another salient feature of theinvention is that the jaw construction is such as to isolate theverticallyoperating hydraulic system from lateral forces whereby theaxial position of the piston is maintained under exceedingly heavyworkpiece tension conditions.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddescription to be read in connection with the accompanying drawingswherein like components in the several views are identified by likereference numerals.

In the drawings:

Fig. 1 is an elevational view of a stretch-forming main which a modifiedform of gripper device is shown;

feature of the invention resides in the fact that the grip- Fig. 6 is anelevational view, partly broken away and partly in section of thegripper device of Fig. 5;

Fig. 7 is an enlarged detail view, shown in elevation,

partly in section, of the lower hydraulic piston and its pivotalconnection to the upper movable jaw of the modified form; I

Fig. 8 is a detail view in elevation of the lower portion of the lowerpiston of the modified form; and

Fig. 9 is a side elevation of Fig. 8. Referring now to the drawings andmore particularly to Fig. 1, a stretch press including gripper devicesin accordance with the invention comprises a die table 10 for supportinga die 11 of suitable shape. Table 10 may be raised or lowered inposition by means including a hydraulic ram, reciprocal in a cylinder 12and controlled by an operator from an instrument console.

The table 10 is located between two gripper devices,

generally designated by numerals 13 and 14, and'includ ing hydrauliccylinders 15 and 16, the devices being designed to engage and holdopposite ends of a workpiece. Gripper devices 13 and 14 are mounted oncarriages 17 and 18, and are tiltable thereon about respective pivotpins 19 and '20 by means of tilting motors 21 and 22. Also provided forthe carriages are lead screws 23 and 24 for adjusting the position ofthe gripper devices longitudinally with respect to the die table. Otherarrangements may be used, such as hydraulic cylinders.

In operation, a workpiece is supported over the die 11 and held alongits opposite side edges by gripper devices 13 and 14. This workpiece ispulled and set permanently in its desired shape by applying tensionincreasing to a point where at least portions of the material are undertensile stresses between its yield point and its ultimate breakingpoint. This operative condition is achieved by restraining or holdingthe opposite edges of the workpiece, or pulling on said edges inopposing directions through the powered movement of the gripper de-.

it to swing 'vertically about the axis .of ther.pin which is;

parallelito. thel'gripper jaws.:-

Seated;on' .anvil 1.26 Z'is a lower fixed. jawpiece 27. in. theformof'racontinuous banext'ending substantially the. 1 The front face of jawpiece.

full length of the anvil. 27- is 'aligned-iwithmthelfront. face ofvanvil' 26 .but .the width of the jaw piece is smallerthan that. of theanvil whereby a channel. 28;is defined between the rear. face of jawpiece 27 and the. adjacentwallof jaw head 25. To secure the jaw pieceagainst displacement with respect to anvilr'26,'. .the:under.:snrface()fithfl jaw piece and .the upper surface .:of .the;.anvil;.'are'=provided :with. complementary serrations: The lower jaw27 isv affixedto. anvil.

26 by means such: as screws 29.

Formed in-jawrpiece 27 is a recess extending the full length thereoffor: accommodating .a series of wearplate inserts :30 at equally spacedpositions .therealong. Co-:

operatively arranged with respect to the lower jaw piece 27 is a movableupper jaw piece 31 in the form. of..a continuous bar extending the fulllength of jaw head 25 and provided with 'a longitudinally extendingrecess 32 for accommodating a series of aligned wear plate .inserts 33at positions corresponding to that of inserts 31 in the lower jaw'pieceand cooperating therewith to grip the margin of a workpiece W-Pto bestretched and shaped over the die. This workpiece may be in-the form ofa metal sheet or bar of uniform or varying shape and contourvasheretofore explained. The'upper inserts 33 are retained in the upperjaw piece by means such as:

screws 34. 1

The movable upper jaw piece 31 is provided with a lip 35 dependingdownwardlytherefrom and dimensioned for insertion in the channel 28behind the lower jaw piece, whereby the. front'face of the lip abuts therear face of the lower jaw piece 27. Lip 35 serves as a guide andstopfor aligning-the edge of the workpiece 33 or any other workpiece tobe gripped and stretched. The lip functions s also to prevent relative.stress and lateral movement in-the direction ofpull during thestretching operation as-between the upper and lower jaws.

To effect downward movement of the upper jaw 31 so as to clamptheworkpiece for stretch-forming, and subsequent upward movement'to releasethe stretched workpiece, a row or bank of main hydraulic pistons 36'isprovided, each of which is reciprocable in respective cylinders 37 boredin jaw head 25.

The upper jaw piece 31 is secured to the lower end or stem of the mainpistons and against the rear face of a shoulder 38depending therefrom bymeans of studs 39. These studs pass through oversize holes 40 in'saidshoulder 'and are threadedly received in the upper jaw piece. Theupper-jaw piece-31 is of deformable metal and r the holes:40 aresomewhat larger in diameter than the studs-39ythus affording thenecessary clearance for relative movement or: playbetweenzthe jaw pieceand the pistons. It :is important to'tnote .that the. lip 35 whichengages the'arear face of the lowerjaw 27 not only actsto-'prevent=-relative movement of the jaw piece but also functions toavoid "lateral displacement of the pistons against the wall-of thecylinder; Thus the lateral pull pressed..npon.the.. dependingv .lip,but. is kept. away. .from

the cylinder, which effect materially improves the hydraulic action.This lip also acts as a locator when inserting sheet or bar stock.

To hold the workpiece W-P tangentially to the sides of the die as it isbeing stretched and shaped, there is connected to the jawhead 25 anose-piece 41 extending substantially the full length' thereof.Nose-piece 41 is attached to jawhead '25. 'by means such as threadedstuds 42. Nose-piece 41 presents a convexly curved surface 43 under and,against whichthe workpiece is placed, the .nose-pie'ce .serving 'as aguide to' the .metal .blank while it is brought to position. It mayeither be-in-the form of a single continuous bar, as shown, extendingsubstantially the fullJ-length of. the jaw head, or it may be ofsectionalized construction consisting of a series of pieces which arearranged end to end in interconnection or articulated.

A row or bank of,hydraulic point units are associated with the upper jaw31 of the gripper device, each unit including, as, already indicated, amain piston 36 reciprocable in a cylinder bore 31 formed injaw head 25.In accordance with the invention these power units are designed to behydraulically actuated in a manner whereby initially a relativelylowpressure is applied and'thereafter, a much higher or intensifiedpressure is applied to develop the necessary gripping forces.

For this purpose, each of cylindrical bores 37 is enclosed at its upperend by a cylinder head 44 which in turn is surmounted by an intensifiercylinder 45 in axial alignment with the lower cylinder bore. Intensifiercylinder 45 is closed at its top by a second cylinder head 46. Cylinderhead 44 and intensifier cylinder 45 are connected together and to jawhead 25 by studs 47.

Cylinder head 44 defines a hydraulic pressure chamber 48 enclosed by thetop of main piston 36 and the side wall of the cylinder. Cylinder head44 has a bore therethrough for the reciprocation therein of anintensifier piston rod 49, the lower end of which has a cylindricalflange 50 extending into a counterbore 51in the piston 36 forreciprocating movement therein. of piston rod 49 is connected to anintensifier piston 52 reciprocable in intensifier cylinder 45. The upperend of counterbore 51 is partially enclosed by a cap 53 secured to mainpiston 36 to provide an abutment for the intensifier piston flange 50 bywhich'said flange is able to lift the main piston and thereby lift theupper jaw 31 during certain phases of operation.

Flange 50 is smaller in diameter than counterbore 51 to define anannular passage 54 for the escape of working liquid therethrough. Thehole in the cap 53 through which the intensifier rod 49 passes isslightly larger in diameter than said rod, thus providing annularclearance 55 around said rod for flow communication with the interior-ofcounterbore 51 and hydraulic pressure chamber 37. Means including pipe56 are provided to feed fluid into the intensifier chamber above theintensifier piston 51. Means including pipes 57 are provided to feedfluid below intensifier piston 52 in the intensifier chamber. Meansincluding pipe 58 are provided to feed fluid above main piston 36 in themain hydraulic chamber.

Asdisclosed in greater detail in the copending application, the main andintensifier cylinders act in conjunction with a hydraulic fluidreservoir and valve system whereby the main cylinder functions to movethe upper jaw into engagement with the lower jaw to grip the workpiece.Means are provided which automatically are operable when the movement ofthe main piston is arrested upon engagement of the movable jaw with theworkpiece for intensifying the hydraulic pressureacting on the mainpiston to enhance the gripping force of the jaws.

In the embodiment of the invention shown in Figs. 5 to 9, the hydraulicactuation system for the jaws may be substantially identical to thatshown in Fig. 1, savefor The upper end the structure of the main piston.Hence this hydraulic system is omitted in Figs. 5 to 9 except for themain piston and its linkage to the upper jaw of the grippers. Basicallythe difference between the gripping devices in Figs. 1 and 5 is that inthe latter the upper jaw structure is sectionalized.

Referring now to Figs. 5 to 9, each of the gripper devices is provided,as in the case of Fig. 1, with a jaw head 25 from which projects ananvil 26 on which is seated a lower fixed jaw piece 27 in the form of acontinuous bar extending the full length of the anvil and coated theretoby means of serrations. Screws 29 serve to hold the lower jaw piece 27in firmly locked relation with the anvil 26.

In place of the spaced inserts shown in the embodiment of Fig. 1, thereis provided a continuous bar or wearplate 60 extending along the fulllength of the low jaw piece, the wearplate being secured to the jawpiece by screws 61. The wearplate has its gripping surface roughened orserrated as at 62 to afford a more positive grip on the blank W-P.

The upper jaw structure is constituted by an assemblage of movable upperjaw sections 63. The movable upper jaw sections receive the motive powerfrom a row of hydraulic main pistons 64, each piston having an upper jawsection 63 depending therefrom. The upper jaw sections are pivotallymounted on the lower end of the pistons in a manner affording enoughplay or free swinging movement to effect alignment with respect to thatpart of the marginal surface which is to be gripped. Each of the upperjaw sections are hydraulically and separately actuated so as to give auniform and direct gripping pressure between the upper and lowergripping jaws, even though the workpiece is tapered, bent or irregularalong its marginal surface to be gripped. In other words, thesectionalized upper jaw is caused generally to assume the configurationof the marginal surface of the workpiece.

The main piston 64 is reciprocal in the hydraulic cylinders 37 formed inthe jaw head 25. The upper jaw sections 63 which constituted the upperjaw assembly extend substantially along the full length of the jaw head25.

The upper jaw sections 63 of each gripper device are pivotally securedto the lower ends of the pistons 64 by headed steel pins 65. The piston64 is provided at its lower end with a centrally located arcuateprojection or rib 66, the rib being dimensioned so as to fit freely intoa similarly shaped recess formed in the upper jaw section to provide aseat 67. The seat 67 is flanked by a pair of ears 68 and 69, each carbeing apertured to receive the shank of a stud pin 65 which also passesthrough an oversized hole 70 in the rib 66. The aperture in car 69 isthreaded to receive the threaded end of the pin 65. The arcuate rib 66and the arcuate seat 67 are of the same radii and are adapted forsliding engagement, thereby coating with the loose-fitting hole toprovide a loose pivotal connection.

In order to reduce friction during the gripping action between the rib66 and its mating seat 67, the center portion of the rib is relievedcentrally, leaving two spaced arcuate lands 71 and 72 to bear on theseat. From this arrangement it will be evident that the pressuretransmitted to the upper jaw section and its serrated insert 73 will bethrough the arcuate seat. The function of stud pin 65 is for the purposeof retracting the upper jaw sections upon opening the grip of the jawsand to permit the loose pivotal movement of the upper jaw section. Topermit this movement, operating clearances 74 are left between adjacentjaw sections.

The gripping inserts 73 are received in recesses in the lower surface ofeach of the upper jaws and are held therein by screws 75. Each upper jawsection has a depending lip portion 76 which is received in a channelbehind the low jaw piece and operates to keep all of the sections inalignment. The lip portions, as previously described, prevent lateraldisplacement of the jaws.

While there has been shown what is considered to be a preferredembodiment of the invention, it will be manifest that many changes andmodifications may be made therein without departing from the essentialspirit of the invention. It is intended, therefore, in the annexedclaims to cover all such changes and modifications as fall within thetrue scope of the invention.

I claim:

1. In a power press for stretch forming metal blanks of widely varyingshape and size, a gripper device for clamping one edge of said blank andcomprising a pair of cooperating jaw structures for holding the blanktherebetween, one of said structures being movable relative to the otherand being constituted by a continuous rectilinear bar of resilientmaterial adapted when clamped on the metal blank to flex so as to assumea profile conforming to the surface of the blank engaged thereby, saidmovable jaw structure being provided at its rear side with a dependinglip portion adapted to set down in back of the other structure to resistdisplacement of said jaws when said blank is subjected to stretchingforces; and apparatus for applying gripping pressure to said movablestructure comprising a row of independent power units formed byhydraulic mechanisms and extending along said movable jaw structure, andmeans loosely coupling each unit to said movable jaw structure to permitsaid structure to assume the desired profile when pressure is appliedthereto.

2. In a power press for stretch forming metal blanks I of widely varyingshape and size, a gripper device for clamping one edge of said blank andcomprising a pair of cooperating jaw structures for holding the blanktherebetween, one of said structures being movable relative to the otherand constituted by a continuous rectilinear bar of resilient materialadapted when clamped on the metal blank to flex so as to assume aprofile conforming to the surface of the blank engaged thereby, saidmovable jaw structure being provided at its rear side with a dependinglip portion adapted to set down in back of the other structure to resistdisplacement of said jaws when said blank is subjected to stretchingforces, and apparatus for applying gripping pressure to said movablestructure comprising a row of hydraulic cylinders extending along saidmovable structure, a piston reciprocable in each cylinder and having ashoulder projecting longitudinally from one end thereof, said bar beingseated against the end of said pistons and laterally against theshoulders thereof, and means loosely coupling said bar to said shouldersto permit said bar to flex with respect to said shoulders and intoconformity with the surface of the blank engaged thereby.

3. In a power press as set forth in claim 2 wherein said loose couplingmeans are constituted by studs conmeeting said shoulders to said bar,said studs passing through oversize bores in said shoulders, wherebysaid bores provide clearance permitting relative movement between thebar and the shoulders.

References Cited in the file of this patent UNITED STATES PATENTS153,133 Van Wagoner July 14, 1874 656,966 Gregory Aug. 28, 1900 878,491Barker Feb. 11, 1908 2,218,503 Brooks et al. Oct. 22, 1940 2,342,437Summers Feb. 22, 1944 2,378,413 Lermont et al. June 19, 1945 2,379,658Saunders July 3, 1945 2,437,105 Lindsey Mar. 2, 1948 2,692,633 GreenOct. 26, 1954 2,696,241 Larsen Dec. 7, 1954 FOREIGN PATENTS 432,766Great Britain Aug. 1, 1935

